Police said a suspect had been arrested following the explosion, which happened at the party office in the centre of The Hague shortly after 9 p.m. local time (1900 GMT), News.Az reports, citing Reuters.
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Dutch Prime Minister Rob Jetten, who is also the leader of D66, said a bomb made of fireworks had been thrown through the letterbox in the frontdoor of the building in what he described as "a cowardly act of intimidation."
The centrist, pro-EU D66 party last year won the election in the Netherlands in a surprise victory over the far right Freedom Party led by nationalist Geert Wilders.
Its head office was also damaged during an anti-immigration protest last year, when protesters smashed the windows of the party seen by many on the far right as serving a progressive elite.
